e Serial Library 

No. 132 

1962 

CONTROL OF RHODODENDRON 

BY BASAL SPRAY 

Rhododendron (Rhododendron maxi?num L.) is a large shrub that 

presents problems in timber management throughout the Appalachian 

Mountains. Although sometimes found in single clumps, rhododendron 

characteristically occurs in extensive dense thickets reaching heights of 

10 feet or more (fig. 1). Of major concern to foresters is the difficulty 

in securing tree regeneration on areas occupied by this shrub. Also, 

because of its prolific growth, rhododendron undoubtedly competes 

severely with existing overstory trees for moisture and nutrients. Except 

where aesthetic values are a consideration, control or eradication is 

definitely desirable. 

The need for control is emphasized by the fact that rhododendron is 

more abundant and vigorous on the better sites. It flourishes on welldrained acid soils in cool, moist locations on shaded mountainsides and 

along stream bottoms; it thrives even in the deep shade of closed 

canopies. It also grows on the tops of high mountains where rainfall is 

heavy and temperatures are moderately low - even on rocky areas of 

shallow soil - but is less objectionable in these places because the sites 

are less productive for timber. 

Rhododendron clumps spread vegetatively by layering and by this 

means coalesce with other clumps to form characteristic thickets. When 

cut, burned, or otherwise disturbed, rhododendron regenerates vigorously 

as stump sprouts, root suckers, and sprouts from layered stems. 
1 Sluder, Earl R. Control of cull trees and weed species in hardwood stands. U. S. Forest Serv. 

Southeast. Forest Expt. Sta., Sta. Paper 95, 13 pp., 1958. 

"c~d equivalent per 100 gallons of mixture. 

2 

The species is comparatively resistant to the commonly used chemical 

herbicides. In 1955, Sluderl tested the following treatments on rhododendron in North Carolina: (1) basal application of a 20-pound ahg2 

mixture of 2,4,5-T in oil; (2) stem cutting only; (3) stem cutting with 

a 20-pound ahg mixture of 2,4,5-T in oil applied to the stumps; and 

(4) stem cutting with ammate crystals applied to the stumps. Only the 

third treatment was effective. 

The same treatments, except for the ammate application, were tested 

later on the Fernow Experimental Forest to check their performance in 

northern West Virginia. The results are reported here. 
Methods and Materials. 

Three treatments and a control were included in the West Virginia 

study. They were: 

The Control, A - no treatment. 

Treatment B - stem cutting only. 

Treatment C - stem cutting and stump spraying with a 20-pound 

ahg mixture of 2,4,5-T in diesel oil. 

Treatment D - basal spraying with the same mixture as in C above. 

The chemicals in Treatments C and D were applied with a hand sprayer. 

Ten rhododendron clumps were included in each treatment. The number of stems per clump, counting major stems and sprouts of all sizes, 

ranged from 1 to 102. Treatments B and C were started in August 1959; 

treatment D was done in April 1960, before the start of the growing 

season. 

Results and Discussion 

Results were analyzed 2 years after treatment (table 1). Two methods 

proved highly successful in controlling rhododendron: cutting followed 

by stump spraying, and basal spraying without cutting. 

Treatment C, stem cutting and stump spraying, is probably 100 percent 

effective when applied thoroughly. Although 19 new sprouts appeared 

after this treatment in 2 of the 10 clumps, these originated probably 

from stumps that were missed or only partly covered in spraying. The 

kills after spraying were mostly quick and unmistakable - rot and bark 

Table 1. - Effect of eradication treatments on rhododendron 

in West Virginia after 2 years 

Live stems 

Treatment* - Increase Decrease 

Before Two years 

treatment after treatment 

No. No. Pelecen t Pevcelzt 

*A = control, no treatment; B = stems cut, no further treatment; C = stems cut and 

stumps sprayed with 2,4,5-T; D = stems basally sprayed with 2,4,5-T. 
slippage became visible within a few weeks. This and the general absence 

of sprouts indicated good chemical penetration and root kill (fig. 2). 

Treatment D, the basal application, was ultimately as effective as 

treatment C. However, treatment D killed relatively slowly. Often only 

the lower branches were affected the first year, which gave the appearance 

of a browse line. The full effect of the treatment became evident only 

after the second growing season (fig. 3). 

Our good results with basal spray in West Virginia were somewhat 

surprising in view of Sluder's poor kills with this treatment in the 

Southeast. These different responses to the same treatment in the two 

regions are inexplicable. Any of several things could be involved, including genetic difference~ within the species, or climatic variables. 

The sprouting ability of rhododendron was revealed in treatment B, 

cutting with no chemical application (fig. 4). This test, and other past 

experience, showed that cutting without additional treatment provides 

Figure 2. -Rhododendron stems cut and stumps sprayed. 

(Treatment C.) 
Figure' 3. - Basal spraying killed this rhododendron clump. 

(Treatment D. ) 
Figure 4. - A year after cutting this rhododendron clump had 

sprouted vigorously. (Treatment B.) 

Figure 5. - Six years after cutting this clump of rhododendron 

was more extensive and vigorous than the original clump, although 

not as tall. 
only temporary control. A few years after cutting treatment new sprouts 

will present an even greater problem than existed before. Figure 5 illustrates the regrowth from one clump 6 years after cutting. 

Although treatment costs could not be determined in a small study 

like this, basal spraying obviously proved a cheaper and easier method 

than cutting and stump spraying. To obtain some measure of the cost 

of basal spraying, a l/lo-acre area of rhododendron thicket was recently 

treated and cost records were kept. This representative plot contained 

more than 12,300 rhododendron stems per acre of all sizes. 

The spray material used was the same as that used in treatment D - 

a 20-pound ahg mixture of 2,4,5-T in diesel oil. Application was by 

hand sprayer. Costs of the treatment were computed only for application 

time, chemical, and carrier. On a per-acre basis, these costs came to 

$137.16. This figure included : 

Labor-30 man-hours at $1.2 5/hr. = $37.50 

Spray material-120 gallons, including: 

6 gallons 2,4,5-T at $13.00/gal. 

114 gallons diesel oil at $0.19/gal. 

Total $137.16 

Because of the small size of the test area, the cost figures are not 

wholly reliable. But even at half the above amount the costs would be 

exorbitant. Basal spraying therefore offers little promise as a practical 

treatment to reduce heavy cover of rhododendron. However, it may be 

a feasible method of eliminating scattered clumps that are just getting 

a toe hold in the woods. 

-HARRY W. YAWNEY 

Research Forester 

Northeastern Forest Experiment Station 

Forest Service, U. S. Dept. Agriculture 

Elkins, W. Va.